As one large-capacity storage battery, a redox flow battery (hereafter also referred to as an “RF battery”) is known (see patent documents 1 and 2). Referred to as applications of the redox flow battery are load leveling, as well as momentary drop compensation and backup power supply, and smoothing an output of natural energy such as solar power generation, wind power generation and the like whose massive introduction is prompted.
An RF battery is a battery which performs charging and discharging using as a positive electrode electrolyte and a negative electrode electrolyte an electrolyte containing a metal ion (an active material) having a valence varying by oxidation-reduction. FIG. 9 shows a principle of an operation of a vanadium-based RF battery 300 which uses as a positive electrode electrolyte and a negative electrode electrolyte a vanadium electrolyte containing a V ion serving as an active material. In FIG. 9 a solid line arrow and a broken line arrow in a battery cell 100 indicate a charging reaction and a discharging reaction, respectively.
RF battery 300 includes cell 100 separated into a positive electrode cell 102 and a negative electrode cell 103 by an ion exchange film 101 which permeates hydrogen ions. Positive electrode cell 102 has a positive electrode 104 incorporated therein, and a tank 106 provided for the positive electrode electrolyte and storing the positive electrode electrolyte is connected via conduits 108, 110 to positive electrode cell 102. Negative electrode cell 103 has a negative electrode 105 incorporated therein, and a tank 107 provided for the negative electrode electrolyte and storing the negative electrode electrolyte is connected via conduits 109, 111 to negative electrode cell 103. And by pumps 112, 113, the electrolyte stored in each tank 106, 107 is circulated and thus passed through cell 100 (positive electrode cell 102 and negative electrode cell 103) to perform charging and discharging.
In RF battery 300, normally, a configuration including a cell stack having a plurality of cells 100 stacked in layers is utilized. FIG. 10 is a schematic configuration diagram of a cell stack. A cell stack 10S illustrated in FIG. 10 is formed such that it is composed of a cell frame 20 including a frame body 22 in the form of a rectangular frame and a bipolar plate 21 provided inside frame body 22, positive electrode 104, ion exchange membrane 101, and negative electrode 105, each stacked in a plurality of layers, and this stack is sandwiched and thus clamped by two end plates 250. Frame body 22 has an opening formed thereinside, and cell frame 20 is such that a recess is formed inside frame body 22 by fitting bipolar plate 21 in the opening of frame body 22. Specifically, cell frame 20 has a recess (a chamber) 24 formed inside frame body 22 by an inner peripheral surface of frame body 22 and a surface of bipolar plate 21, and positive electrode 104 is disposed at one surface side of bipolar plate 21 and negative electrode 105 is disposed at the other surface side of bipolar plate 21. Frame body 22 shown in FIG. 10 by way of example is in the form of a rectangular frame composed of a pair of opposite, upper and lower long pieces 22L and a pair of right and left short pieces 22S which connect the ends of long pieces 22L. In chamber 24 formed inside frame body 22, electrodes (positive electrode 104 or negative electrode 105) are accommodated, and an internal space of chamber 24 surrounded by bipolar plate 21, frame body 22, and ion exchange membrane 101 configures a cell (a positive electrode cell or a negative electrode cell). In the above cell stack 10S, as shown in FIG. 10, a single cell (a unit cell) 100 will be formed by disposing a pair of positive and negative electrodes 104, 105 between adjacent cell frames 20 with ion exchange membrane 101 interposed between the electrodes.
In cell stack 10S, an electrolyte is passed by a manifold 200 formed in and penetrating frame body 22, and a slit 210 formed on a surface of frame body 22 and providing connection between manifold 200 and chamber 24. Slit 210 has one end connected to manifold 200 and the other end connected to chamber 24. In cell stack 10S illustrated in FIG. 10, the positive electrode electrolyte is supplied from a liquid supply manifold 201 via a liquid supply slit 211 that is formed in one surface side (corresponding to the front side of the sheet of the drawing) of frame body 22 to chamber 24 having positive electrode 104 accommodated therein, passes through chamber 24, and is drained via a liquid drainage slit 213 to a liquid drainage manifold 203. Similarly, the negative electrode electrolyte is supplied from a liquid supply manifold 202 via a liquid supply slit 212 that is formed in the other surface side (corresponding to the back side of the sheet of the drawing) of frame body 22 to the chamber having negative electrode 105 accommodated therein, and is drained via a liquid drainage slit 214 to a liquid drainage manifold 204. Between cell frames 20, in order to suppress leakage of the electrolyte, a looped seal member 50, such as an O ring and a flat gasket, is disposed along an outer perimeter of frame body 22.